The disclosure relates, in general, to radiation filters and, more particularly, to radiation filters for use with external beam radiation systems.
Conventional external beam radiation therapy, also referred to as “teletherapy,” is commonly administered by directing a linear accelerator (“LINAC”) to produce beams of ionizing radiation that irradiates the defined target volume in a patient. The radiation beam is a single beam of radiation that is delivered to the target region from several different directions, or beam paths. Together, the determination of how much dose to deliver along each of these beam paths constitutes the so-called radiation therapy “plan.” The purpose of the treatment plan is to accurately identify and localize the target volume in the patient that is to be treated.
Intensity modulated radiation therapy (“IMRT”) is an external beam radiation therapy technique that utilizes computer planning software to produce a three-dimensional radiation dose map, specific to a target tumor's shape, location, and motion characteristics. Various regions within a tumor and within the patient's overall anatomy may receive varying radiation dose intensities through IMRT, which treats a patient with multiple rays of radiation, each of which may be independently controlled in intensity and energy. Each of these rays or beams is composed of a number of sub-beams or beamlets, which may vary in their individual intensity, thereby providing the overall intensity modulation. Because of the high level of precision required for IMRT methods, detailed data must be gathered about tumor locations and their motion characteristics. In doing so, the radiation dose imparted to healthy tissue can be reduced while the dose imparted to the affected region, such as a tumor, can be increased. In order to achieve this, accurate geometric precision is required during the treatment planning stage.
Image-guided radiation therapy (“IGRT”) employs medical imaging, such as computed tomography (“CT”), concurrently with the delivery of radiation to a subject undergoing treatment. In general, IGRT is employed to accurately direct radiation therapy using positional information from the medical images to supplement a prescribed radiation delivery plan. The advantage of using IGRT is twofold. First, it provides a means for improved accuracy of the radiation field placement. Second, it provides a method for reducing the dose imparted to healthy tissue during treatment. Moreover, the improved accuracy in the delivery of the radiation field allows for dose escalation in the tumor, while mitigating dose levels in the surrounding healthy tissue.
In general, flattening filters (FF) have been included as a component of LINAC systems over the past decades. Moreover, flattening-filter-free (FFF) treatment beams have been studied and implemented in recent years. FFF treatment beams offer distinct advantages such as higher dose rate and rapid beam modulation in advanced radiation therapy techniques such as IMRT, stereotactic body radiation therapy (SBRT) and gated treatment (GT). In one aspect, the FFF beam may limit the scatter generated by the FF within the gantry head. The reduced scatter can potentially benefit the dose sparing effect to peripheral organs. However, the soft spectrum of the FFF beam may increase the superficial and internal scatter dose in a patient's body and potentially compromise the dose sparing effect. Accordingly there is a need for systems and methods that overcome one or more of the aforementioned problems.